The word 可是 is formed through the historical fusion and semantic shift of its two component characters. The character 可 originally carries a sense of "can" or "may", implying affirmation or permission, while 是 means "to be" or "this", indicating correctness or reality. When combined, their literal meanings of "can be this" evolved through classical usage into a logical pivot, where the affirmed first clause introduced by 可 is subtly countered or contrasted by what follows, effectively blending "yes, but"... into a single concessive conjunction that sets up a contradiction or exception.